Heat engine and heat to electricity systems and methods with working fluid fill system

ABSTRACT

A waste heat recovery system and a method for operating a thermodynamic cycle using a working fluid in a working fluid circuit which has a high pressure side and a low pressure side. The system comprises a waste heat exchanger, a waste heat source, an expander, a recuperator, a cooler, a pump, and a mass management system connected to the working fluid circuit. The mass management system comprises a working fluid vessel connected to the low pressure side of the working fluid circuit and configured to passively control an amount of working fluid mass in the working fluid circuit.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 12/631,379, filed Dec. 4, 2009, now issued as U.S. Pat. No.8,096,128, which claims the benefit of U.S. provisional patentapplication Ser. No. 61/243,200, filed Sep. 17, 2009.

FIELD OF THE INVENTION

This disclosure and the related inventions are in the general field ofthermodynamics and energy conversion systems and methods.

BACKGROUND OF THE INVENTION

Heat is often created as a byproduct of industrial processes whereflowing streams of liquids, solids or gasses that contain heat must beexhausted into the environment or removed in some way in an effort tomaintain the operating temperatures of the industrial process equipment.Sometimes the industrial process can use heat exchanger devices tocapture the heat and recycle it back into the process via other processstreams. Other times it is not feasible to capture and recycle this heatbecause it is either too high in temperature or it may containinsufficient mass flow. This heat is referred to as “waste” heat. Wasteheat is typically discharged directly into the environment or indirectlythrough a cooling medium, such as water.

Waste heat can be utilized by turbine generator systems which employ awell known thermodynamic method known as the Rankine cycle to convertheat into work. Typically, this method is steam-based, wherein the wasteheat is used to create steam in a boiler to drive a turbine. Thesteam-based Rankine cycle is not always practical because it requiresheat source streams that are relatively high in temperature (600° F. orhigher) or are large in overall heat content. The complexity of boilingwater at multiple pressures/temperatures to capture heat at multipletemperature levels as the heat source stream is cooled, is costly inboth equipment cost and operating labor. The steam-based Rankine cycleis not a realistic option for streams of small flow rate and/or lowtemperature.

There exists a need in the art for a system that can efficiently andeffectively produce power from not only waste heat but also from a widerange of thermal sources.

SUMMARY OF THE INVENTION

A waste heat recovery system executes a thermodynamic cycle using aworking fluid in a working fluid circuit which has a high pressure sideand a low pressure side. Components of the system in the working fluidcircuit include a waste heat exchanger in thermal communication with awaste heat source also connected to the working fluid circuit, wherebythermal energy is transferred from the waste heat source to the workingfluid in the working fluid circuit, an expander located between the highpressure side and the low pressure side of the working fluid circuit,the expander operative to convert a pressure/enthalpy drop in theworking fluid to mechanical energy, a recuperator in the working fluidcircuit operative to transfer thermal energy between the high pressureside and the low pressure side of the working fluid circuit, a cooler inthermal communication with the low pressure side of the working fluidcircuit operative to control temperature of the working fluid in the lowside of the working fluid circuit, a pump in the working fluid circuitand connected to the low pressure side and to the high pressure side ofthe working fluid circuit and operative to move the working fluidthrough the working fluid circuit, and a mass management systemconnected to the working fluid circuit, the mass management systemhaving a working fluid vessel connected to the low pressure side of theworking fluid circuit.

The disclosure and related inventions further address the need to fill awaste heat recovery or heat engine system having a mass managementsystem with working fluid by providing a fill system that fills the massmanagement system of the heat engine system with working fluid. Theinventive fill system comprises a fill storage tank (vessel) which inone embodiment is not in direct fluid communication with the circulationloop of the heat engine system; rather the storage tank is in directfluid communication with a mass management system of the heat enginesystem and most preferably the mass control tank (also referred toherein as a mass management tank) or working fluid vessel of the massmanagement system.

In a preferred embodiment, the fill storage tank is capable of storingworking fluid at a pressure and temperature that is convenient forstorage; in the preferred embodiment the working fluid is carbon dioxideand the preferred storage temperature is between 8-24 degrees F. and thepreferred storage pressure is between 200-350 psia. The fill system isalso comprised of conduit, or “working fluid supply line”, suitable fortransferring the working fluid between the fill storage tank and themass management system's mass control tank and one or more valves influid communication with such conduit to regulate the flow of massbetween the two storage tanks.

The inventive fill system moves working fluid from the fill storage tankto the mass management system by utilizing a pressure differentialbetween working fluid in the fill storage tank (vessel), in a preferredembodiment this vessel may be a dewar D or bulk storage tank, and theworking fluid in the mass control tank. In the inventive system, thispressure differential drives working fluid into the mass control tank.Also, as further described a pump may be provided in the conduitextending between the fill storage tank and the mass control tank whichenables movement of working fluid against the pressure differential.

In a preferred embodiment, the mass storage tank for the mass managementsystem further includes a means (such as but not limited to athermocouple) for measuring the temperature of the working fluid withinthe mass storage tank at both the tank inlet near the bottom of the tankand at the top of the tank in order to measure when the tank is full andcontrol instrumentation that communicates with the one or more valvesbetween the fill storage tank and the mass management storage tank. Themass storage tank further includes a means for measuring the fill heightof the working fluid within a mass storage tank (such as but not limitedto a dip tube) and control instrumentation that communicates with themass storage tank and the heat engine system; alternatively, theinventive fill system provides a means for determining how much workingfluid moved into the mass management system such as but not limited to amass reading instrument (e.g., a scale), one or more pressure sensors,or a flow meter.

The mass management storage tank may further include a heat source forapplying heat to the stored working fluid and instrumentation incommunication with the heat source for regulating the application ofheat to the working fluid within mass storage tank.

A waste heat recovery system executes a thermodynamic cycle using aworking fluid in a working fluid circuit which has a high pressure sideand a low pressure side. Components of the system in the working fluidcircuit include a waste heat exchanger in thermal communication with awaste heat source also connected to the working fluid circuit, wherebythermal energy is transferred from the waste heat source to the workingfluid in the working fluid circuit, an expander located between the highpressure side and the low pressure side of the working fluid circuit,the expander operative to convert a pressure/enthalpy drop in theworking fluid to mechanical energy, a recuperator in the working fluidcircuit operative to transfer thermal energy between the high pressureside and the low pressure side of the working fluid circuit, a cooler inthermal communication with the low pressure side of the working fluidcircuit operative to control temperature of the working fluid in the lowside of the working fluid circuit, a pump in the working fluid circuitand connected to the low pressure side and to the high pressure side ofthe working fluid circuit and operative to move the working fluidthrough the working fluid circuit, and a mass management systemconnected to the working fluid circuit, the mass management systemhaving a working fluid vessel connected to the low pressure side of theworking fluid circuit, and a fill system to move working fluid stored ina fill storage tank into and/or out of the mass management system of thecycle.

In one embodiment, a waste heat energy recovery and conversion deviceincludes a working fluid circuit having conduit and components forcontaining and directing flow of a working fluid between components ofthe device operative to convert thermal energy into mechanical energy,the working fluid circuit having a high pressure side and a low pressureside; a support structure for supporting the conduit of the workingfluid circuit and the components, the components comprising: an expanderoperative to convert a pressure drop in the working fluid to mechanicalenergy, a power generator (such as for example an alternator) which iscoupled to the expander, a recuperator, a cooler, a pump and a pumpmotor operative to power the pump; and a mass management system having amass control tank for receiving and holding the working fluid, the masscontrol tank connected by conduit to the high pressure side of theworking fluid circuit and to the low pressure side of the working fluidcircuit. An enclosure may also be provided to substantially enclose someor all of the components of the device. One or more heat exchangers maybe located on or off of the support structure. The heat exchanger(s),recuperator and cooler/condenser may include printed circuit heatexchange panels. A control system for controlling operation of thedevice may be remote or physically packaged with the device.

The disclosure and related inventions further includes a method ofconverting thermal energy into mechanical energy by use of a workingfluid in a closed loop thermodynamic cycle contained in a working fluidcircuit having components interconnected by conduit, the componentsincluding at least one heat exchanger operative to transfer thermalenergy to the working fluid, at least one expansion device operative toconvert thermal energy from the working fluid to mechanical energy, atleast one pump operative to transfer working fluid through the workingfluid circuit, the working fluid circuit having a high pressure side anda low pressure side, and a mass management system comprising a massmanagement vessel connected by conduit to the low pressure side of theworking fluid circuit, the method including the steps of: placing athermal energy source in thermal communication with a heat exchangercomponent; pumping the working fluid through the working fluid circuitby operation of the pump to supply working fluid in a supercritical orsubcritical state to the expander; directing the working fluid away fromthe expander in a sub-critical state through the working fluid circuitand to the pump; controlling flow of the working fluid in asuper-critical state from the high pressure side of the working fluidcircuit to the mass management vessel, and controlling an amount ofworking fluid in a sub-critical or super-critical state from the massmanagement vessel to the low pressure side of the working fluid circuitand to the pump.

The disclosure and related inventions further includes a mass managementsystem for controlling an amount of working fluid mass in athermodynamic cycle in a working fluid circuit having a pump or acompressor, the mass management system having a working fluid controltank for holding an amount of the working fluid at a first pressure P,the working fluid control tank located outside of the working fluidcircuit; and a fluid connection between the working fluid control tankand a low pressure side of the thermodynamic cycle in the working fluidcircuit to allow passage of the working fluid between the working fluidcircuit and the working fluid control tank.

These and other aspects of the disclosure and related inventions arefurther described below in representative forms with reference to theaccompanying drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the heat to electricity system of thepresent invention;

FIG. 2 is a pressure-enthalpy diagram for carbon dioxide;

FIGS. 3A-3M are schematic drawings of a representative embodiment of aheat engine device and heat engine skid of the present disclosure andrelated inventions;

FIG. 4A is a flow chart of operational states of a heat engine of thedisclosure;

FIG. 4B is a flow chart representing a representative start-up andoperation sequence for a heat engine of the disclosure;

FIG. 4C is a flow chart representing a shut-down sequence for a heatengine of the disclosure;

FIG. 5A is a schematic of a working fluid fill system of the presentdisclosure;

FIG. 5B is a schematic of a heat engine system having a working fluidcircuit with a working fluid fill system of the present disclosure;

FIG. 5C is a schematic of a heat engine system having a working fluidcircuit showing an embodiment of the working fluid fill system of thepresent disclosure, and

FIG. 5D is a schematic of a heat engine system having a working fluidcircuit showing an embodiment of the working fluid fill system of thepresent disclosure.

DETAILED DESCRIPTION OF PREFERRED AND ALTERNATE EMBODIMENTS

The inventive heat engine 100 (also referred to herein in thealternative as a “thermal engine”, “power generation device”, “wasteheat recovery system” and “heat recovery system”, “heat to electricitysystem”) of the present disclosure utilizes a thermodynamic cycle whichhas elements of the Rankine thermodynamic cycle in combination withselected working fluid(s), such as carbon dioxide, to produce power froma wide range of thermal sources. By “thermal engine” or “heat engine”what is generally referred to is the equipment set that executes thethermodynamic cycle described herein; by “heat recovery system” what isgenerally referred to is the thermal engine in cooperation with otherequipment to deliver heat (from any source) to and remove heat from theinventive thermal engine.

The thermodynamic cycle executed by the heat engine 100 is describedwith reference to a pressure-enthalpy diagram for a selected workingfluid, FIG. 2. The thermodynamic cycle is designed to operate as aclosed loop thermodynamic cycle in a working fluid circuit having a flowpath defined by conduit which interconnects components of the workingfluid circuit. The thermal engine which operates the cycle may or maynot be hermetically or otherwise entirely sealed (such that no amount ofworking fluid is leaked from the system into the surroundingenvironment).

The thermodynamic cycle that is executed by the thermal engine is shownin its most rudimentary form in FIG. 2 which is a pressure-enthalpydiagram for carbon dioxide. The thermodynamic cycle may be described forease of understanding by referencing a working fluid at point A on thisdiagram. At this point, the working fluid has its lowest pressure andlowest enthalpy relative to its state at any other point during thecycle and as shown on the diagram. From there, the working fluid iscompressed and/or pumped to a higher pressure (point B on the diagram).From there, thermal energy is introduced to the working fluid which bothincreases the temperature of the working fluid and increases theenthalpy of the working fluid (point C on the diagram). The workingfluid is then expanded through a mechanical process to point (D). Fromthere, the working fluid discharges heat, dropping in both temperatureand enthalpy, until it returns to point (A). Each process (i.e., A-B,B-C, C-D, D-A) need not occur as shown on the exemplary diagram and oneof ordinary skill in the art would recognize that each step of the cyclecould be achieved in a variety of ways and/or that it is possible toachieve a variety of different coordinates on the diagram. Similarly,each point on the diagram may vary dynamically over time as variableswithin and external to the system change, i.e., ambient temperature,waste heat temperature, amount of mass in the system.

In the preferred embodiment of the thermal engine, the cycle is executedduring normal, steady state operation such that the low pressure side ofthe system (points A and D on FIG. 2) is between 400 psia and 1500 psiaand the high pressure side of the system is between 2500 psia and 4500psia (points B and C FIG. 2). One of ordinary skill in the art wouldrecognize that either or both higher or lower pressures could beselected for each or all points. In the preferred embodiment of thecycle, it will be observed that between points C and D, the workingfluid transitions from a supercritical state to a subcritical state(i.e., a transcritical cycle); one of ordinary skill in the art wouldrecognize that the pressures at points C and D could be selected suchthat the working fluid remained in a supercritical state during theentire cycle.

In a preferred embodiment of the thermal engine, the working fluid iscarbon dioxide. The use of the term carbon dioxide is not intended to belimited to carbon dioxide of any particular type, purity or grade ofcarbon dioxide although industrial grade carbon dioxide is the preferredworking fluid. Carbon dioxide is a greenhouse friendly and neutralworking fluid that offers benefits such as non-toxicity,non-flammability, easy availability, low price, and no need ofrecycling.

In the preferred embodiment, the working fluid is in a supercriticalstate over certain portions of the system (the “high pressure side”),and in a subcritical state at other portions of the system (the “lowpressure side”). In other embodiments, the entire cycle may be operatedsuch that the working fluid is in a supercritical or subcritical stateduring the entire execution of the cycle.

In various embodiments, the working fluid may a binary, ternary or otherworking fluid blend. The working fluid combination would be selected forthe unique attributes possessed by the fluid combination within a heatrecovery system as described herein. For example, one such fluidcombination is comprised of a liquid absorbent and carbon dioxideenabling the combined fluid to be pumped in a liquid state to highpressure with less energy input than required to compress CO₂. Inanother embodiment, the working fluid may be a combination of carbondioxide and one or more other miscible fluids. In other embodiments, theworking fluid may be a combination of carbon dioxide and propane, orcarbon dioxide and ammonia.

One of ordinary skill in the art would recognize that using the term“working fluid” is not intended to limit the state or phase of matterthat the working fluid is in. In other words, the working fluid may bein a fluid phase, a gas phase, a supercritical phase, a subcriticalstate or any other phase or state at any one or more points within thecycle.

The inventive heat to electricity system may utilize other fluids inother parts of the system, such as water, thermal oils or suitablerefrigerants; these other fluids may be used within heat exchangers andequipment external to the heat engine 100 (such as at the Cooler 12and/or Waste Heat Exchanger 5 shown in FIG. 1) and within cooling orother cycles and subsystems that operate within the heat to electricitysystem (for example at the Radiator 4 cooling loop provided at thealternator 2 of the thermal engine shown in FIG. 1).

As further described, in one representative embodiment, a 250 kW (net)or greater skid-based system, as illustrated conceptually in FIGS.3A-3M, is provided for deployment at any source or site of waste orby-product heat. Nominal rated output (electrical or work) is notintended to be a limiting feature of the disclosure or relatedinventions.

The heat engine 100 of the disclosure has three primary classes ofequipment through which the working fluid may be circulated as thethermodynamic cycle is executed, (i) one or more heat exchangers (ii)one or more pumps and/or compressors and (iii) one or more expansion(work) devices (Such as a turbine, a ramjet, or a positive displacementexpander 3 such as a geroler or gerotor). Each of these pieces ofequipment is operatively coupled in the cycle as shown on FIG. 1 throughthe use of suitable conduits, couplings and fittings, for example in aworking fluid circuit, as further described.

The heat engine 100 may also include a means for converting mechanicalenergy from the one or more expansion devices into electricity; suchmeans may include but are not limited to a generator, alternator 2, orother device(s) and related power conditioning or conversion equipmentor devices.

In one embodiment, certain components of the heat engine 100 may sharecommon elements such as in the case of a turboalternator (shown onFIG. 1) (where an expansion device shares a common shaft with analternator 2) or in the case of a turbopump, where an expansion deviceshares a common shaft with a pump. Alternatively, the expansion devicemay be mechanically coupled to the electrical generating means (i) bymagnetically coupling the turbine shaft to the rotor of the electricalgenerating means and/or (ii) by a gearbox operatively coupling theturbine shaft and the rotor of the electrical generating means.

The heat engine 100 may also include other equipment and instrumentssuch as sensors, valves (which may be on/off or variable), fittings,filters, motors, vents, pressure relief equipment, strainers, suitableconduit, and other equipment and sensors. The preferred heat engine 100includes the additional equipment shown on FIG. 1.

The preferred heat engine 100 also includes a system for managing theamount of working fluid within the system such as the mass managementsystem disclosed on FIG. 1, as further described.

The preferred heat engine 100 also includes a control system and relatedequipment allowing for the automated and/or semi-automated operation ofthe engine, the remote control of the system and/or the monitoring ofsystem performance.

The preferred heat engine 100 also includes one or more cooling cyclesystems to remove heat from and/or provide thermal management to one ormore of the expansion device, the electrical producing means and/or thepower electronics 1. In the preferred embodiment, there is provided acooling cycle shown on FIG. 1 that removes heat from and providesthermal management to the mechanical coupling between the expander 3 andthe alternator 2, the alternator 2, and the power electronics 1.

The system of the current invention is flexible and may utilize manydifferent types of conventional heat exchangers. The preferredembodiment of the inventive heat engine system 100 utilizes one or moreprinted circuit heat exchangers (PCHE) or other construction of the heatexchanger, recuperator or cooler components, each of which may containone or more cores where each core utilizes microchannel technology.

As used herein and known in the art, “microchannel technology” includes,but is not limited to, heat exchangers that contain one or moremicrochannels, mesochannels, and/or minichannels. As used herein theterms “microchannels,” “mesochannels,” and/or “minichannels” areutilized interchangeably. Additionally, the microchannels, mesochannels,and/or minichannels of the present invention are not limited to any oneparticular size, width and/or length. Any suitable size, width or lengthcan be utilized depending upon a variety of factors. Furthermore, anyorientation of the microchannels, mesochannels, and/or minichannels canbe utilized in conjunction with the various embodiments of the presentinvention.

The expansion device (also referred to herein as an “expander”) may be avalve or it may be a device capable of transforming high temperature andpressure fluid into mechanical energy. The expansion device may have anaxial or radial construction; it may be single or multi-staged. Examplesinclude a geroler, a gerotor, other types of positive displacementdevices such as a pressure swing, a turbine, or any other device capableof transforming a pressure or pressure/enthalpy drop in a working fluidinto mechanical energy.

In a preferred embodiment, the device 3 is a turboalternator wherein theturbine is operatively coupled to the alternator 2 by either (i) sharinga single shaft (the “single shaft design”) or by operatively couplingthe turbine shaft to the alternator 2 rotor (or other shaft) by usinghigh powered magnets to cause two shafts to operate as a single shaft.In the preferred embodiment, the turbine is physically isolated from thealternator 2 in order to minimize windage losses within the alternator2. Thus, in the preferred embodiment, while the turbine is operativelycoupled to the alternator 2, the turbine and alternator 2 do not share acommon housing (or casing). In the single shaft design, the turbinecasing is sealed at the common shaft and thereby isolated from thealternator 2 through the use of suitable shaft seals. In the singleshaft design, suitable shaft seals may be any of the following,labyrinth seal, a double seal, a dynamically pressure balanced seal(sometimes called a floating ring or fluid filled seal), a dry gas sealor any other sealing mechanism. In the magnetic coupling design, noshaft seals are required because it is possible to entirely encase theturbine within its housing thereby achieving the desired isolation fromthe alternator 2.

Among other differentiating attributes of the preferred turboalternatorare its single axis design, its ability to deliver high isentropicefficiency (>70%), that it operates at high rotational speeds (>20Krpm), that its bearings are either not lubricated during operation orlubricated during operation only by the working fluid, and itscapability of directly coupling a high speed turbine and alternator 2for optimized system (turboalternator) efficiency. In the preferredembodiment, the turboalternator uses air-foil bearings; air foilbearings are selected as the preferred design due because they reduce oreliminate secondary systems and eliminate the requirement forlubrication (which is particularly important when working with thepreferred working fluid, carbon dioxide). However, hydrostatic bearings,aerostatic hearings, magnetic bearings and other bearing types may beused.

The heat engine 100 also provides for the delivery of a portion of theworking fluid into the expander 3 chamber (or housing) for purposes ofcooling one or more parts of the expander 3. In a preferred embodiment,due to the potential need for dynamic pressure balancing within thepreferred heat engine's turboalternator, the selection of the sitewithin the thermal engine from which to obtain this portion of theworking fluid is critical because introduction of the portion of theworking fluid into the turboalternator must not disturb the pressurebalance (and thus stability) of the turboalternator during operation.This is achieved by matching the pressure of the working fluid deliveredinto the turboalternator for purposes of cooling with the pressure ofthe working fluid at the inlet of the turbine; in the preferred heatengine 100, this portion of the working fluid is obtained after theworking fluid passes a valve 25 and a filter F4. The working fluid isthen conditioned to be at the desired temperature and pressure prior tobeing introduced into the turboalternator housing. This portion of theworking fluid exits the turboalternator at the turboalternator outlet. Avariety of turboalternator designs are capable of working within theinventive system and to achieve different performance characteristics.

The device for increasing the pressure of the working fluid from pointA-B on FIG. 2 may be a compressor, pump, a ramjet type device or otherequipment capable of increasing the pressure of the selected workingfluid. In a preferred embodiment, the device is a pump 9, as depicted inFIG. 1. The pump 9 may be a positive displacement pump, a centrifugalpump or any other type or construction of pump.

The pump 9 may be coupled to a VFD (variable frequency drive) 11 tocontrol speed which in turn can be used to control the mass flow rate ofthe working fluid in the system, and as a consequence of this controlthe high side system pressure. The VFD may be in communication with acontrol system, as further described.

In another embodiment of the inventive thermal engine, the pump 9 may beconstructed such that there is a common shaft (not shown) connecting itwith an expansion device enabling the pump to be driven by themechanical energy generated by expansion of the working fluid (e.g., aturbopump). A turbopump may be employed in place of or to supplement thepump of the preferred embodiment. As noted in the section abovedetailing the turboalternator, the “common shaft” may be achieved byusing a magnetic coupling between the expansion device's shaft and thepump shaft. In one embodiment of the heat engine 100 with a turbopump,there is provided a secondary expansion device that is coupled to thepump by a common shaft. The secondary expansion device is located withina stream of fluid which runs parallel to the stream to the primarysystem expander 3 and there are two valves on either side of thesecondary expander to regulate flow to the second expander. It should benoted that there need not be a second expander in order to form aturbopump. The common shaft of the turbopump may be shared with thecommon shaft of the primary system expander 3 and/or, in a preferredembodiment, the common shaft of the turboalternator. Similarly, if thesystem uses a secondary expansion device to share a common shaft withthe turbopump, the secondary expansion device need not be located asdescribed above.

The electrical producing means of one embodiment of the thermal engineis a high speed alternator 2 that is operatively coupled to the turbineto form a turboalternator (as described above). The electrical producingmeans may alternatively be any known means of converting mechanicalenergy into electricity including a generator or alternator 2. It may beoperatively coupled to the primary system expander 3 by a gear box, bysharing a common shaft, or by any other mechanical connection.

The electrical producing means is operatively connected to powerelectronics 1 equipment set. In the preferred embodiment, the electricaloutput of the alternator 2 is mated with a high efficiency powerelectronics 1 equipment set that has equipment to provide active loadadjustment capability (0-100%). In the preferred embodiment, the powerelectronics 1 system has equipment to provide the capability to converthigh frequency, high voltage power to grid-tic quality power atappropriate conditions with low total harmonic distortion (THD), SAGsupport, current and voltage following, VAR compensation, for providingtorque to start the turboalternator, and dynamic braking capability forversatile and safe control of the turboalternator in the event of loadloss; it has also capability of synchronizing and exporting power to thegrid for a wide voltage and speed range of the alternator 2. In thepreferred embodiment, the pump 9 inlet pressure has a direct influenceon the overall system efficiency and the amount of power that can begenerated. Because of the thermo-physical properties of the preferredworking fluid, carbon dioxide, as the pump 9 inlet temperature rises andfalls the system must control the inlet pressure over wide ranges ofinlet pressure and temperature (for example, from −4 deg F. to 104 degF.; and 479 psia to 1334 psia). In addition, if the inlet pressure isnot carefully controlled, pump 9 cavitation is possible.

A mass management system is provided to control the inlet pressure atthe pump 9 by adding and removing mass from the system, and this in turnmakes the system more efficient. In the preferred embodiment, the massmanagement system operates with the system semi-passively. The systemuses sensors to monitor pressures and temperatures within the highpressure side (from pump 9 outlet to expander 3 inlet) and low pressureside (from expander 3 outlet to pump 9 inlet) of the system. The massmanagement system may also include valves, tank heaters or otherequipment to facilitate the movement of the working fluid into and outof the system and a mass control tank 7 for storage of working fluid.

As shown on FIG. 1, in the case of the preferred embodiment, the massmanagement system includes the equipment operatively connected by thebolded lines or conduits of the diagram and at (and including) equipmentat the termination points of the mass control system (e.g., 14, 15, 16,17, 18, 21, 22, and 23). The preferred mass management system removeshigher pressure, denser working fluid (relative to the pressure,temperature, and density on the low pressure side of the system) fromthe thermodynamic cycle being executed by the thermal engine via valve16. The mass management system dispenses working fluid into the mainheat engine system 100 via valves 14 and 15. By controlling theoperation of the valves 14, 15 and 16, the mass management system addsor removes mass from the system without a pump, reducing system cost,complexity and maintenance.

In the preferred embodiment of the system, the Mass Control Tank 7 isfilled with working fluid. It is in fluid communication with valves 14and 16 such that opening either or both valve valves 14, 16 will deliverworking fluid to the top of the Mass Control Tank 7. The Mass ControlTank 7 is in fluid communication with valve 15 such that opening valve15 will remove working fluid from the bottom of the Mass Control Tank 7.The working fluid contained within the Mass Control Tank 7 will stratifywith the higher density working fluid at the bottom of the tank and thelower density working fluid at the top of the tank. The working fluidmay be in liquid phase, vapor phase or both; if the working fluid is inboth vapor phase and liquid phase, there will be a phase boundaryseparating one phase of working fluid from the other with the denserworking fluid at the bottom of the Mass Control Tank 7. In this way,valve 15 will also deliver to the system the densest working fluidwithin the Mass Control Tank 7.

In the case of the preferred embodiment, this equipment set is combinedwith a set of sensors within the main heat engine system 100 and acontrol system as described within.

In the case of the preferred embodiment, this mass management systemalso includes equipment used in a variety of operating conditions suchas start up, charging, shut-down and venting the heat engine system 100as shown on FIG. 1.

Exemplary operation of the preferred embodiment of the mass managementsystem follows. When the working fluid in the mass control tank 7 is atvapor pressure for a given ambient temperature, and the low sidepressure in the system is above the vapor pressure, the pressure in themass control tank 7 must be increased, to allow for the addition of massinto the system. This can be controlled by opening the valve and therebyallowing higher pressure, higher temperature, lower densitysupercritical working fluid to flow into the mass control tank 7. Valve15 is opened to allow higher density liquid working fluid at the bottomof the mass control tank 7 to flow into the system and increase pump 9suction pressure.

The working fluid may be in liquid phase, vapor phase or both. If theworking fluid is in both vapor phase and liquid phase, there will be aphase boundary in the mass control tank 7. In general, the mass controltank 7 will contain either a mixture of liquid and vapor phase workingfluid, or a mass of supercritical fluid. In the former case, there willbe a phase boundary. In the latter case, there will not be a phaseboundary (because one does not exist for supercritical fluids). Thefluid will still tend to stratify however, and the valve 15 can beopened to allow higher density liquid working fluid at the bottom of themass control tank 7 to flow into the system and increase pump suctionpressure. Working fluid mass may be added to or removed from the workingfluid circuit via the mass control tank 7.

The mass management system of the disclosure may be coupled to a controlsystem such that the control of the various valves and other equipmentis automated or semi-automated and reacts to system performance dataobtained via sensors located throughout the system, and to ambient andenvironmental conditions.

Other configurations for controlling pressure and/or temperature (orboth) in the mass control tank 7 in order to move mass in and out of thesystem (i.e., the working fluid circuit), include the use of a heaterand/or a coil within the vessel/tank or any other means to add or removeheat from the fluid/vapor within the mass control tank 7. Alternatively,mechanical means, such as providing pump may be used to get workingfluid from the mass control tank 7 into the system.

One method of controlling the pressure of the working fluid in the lowside of the working fluid circuit is by control of the temperature ofthe working fluid vessel or mass control tank 7. A basic requirement isto maintain the pump 9 inlet pressure above the boiling pressure at thepump 9 inlet. This is accomplished by maintaining the temperature of themass control tank 7 at a higher level than the pump 9 inlet temperature.Exemplary methods of temperature control of the mass control tank 7 are:direct electric heat; a heat exchanger coil with pump 9 discharge fluid(which is at a higher temperature than at the pump 9 inlet), or a heatexchanger coil with spent cooling water from the cooler/condenser (alsoat a temperature higher than at the pump 9 inlet).

As shown in FIGS. 3A-3M, with continuing reference to FIG. 1, the wasteheat recovery system of the disclosure may be constructed in one formwith the primary components described and some or all of which may bearranged on a single skid or platform or in a containment or protectiveenclosure, collectively referred to herein as a “skid” or “supportstructure”. FIGS. 3A-3M illustrate a representative embodiment of theinventive heat engine 100 with exemplary dimensions, port locations, andaccess panels. Some of the advantages of the skid type packaging of theinventive heat engine 100 include general portability and installationaccess at waste heat sources, protection of components by the externalhousing, access for repair and maintenance, and ease of connection tothe inventive heat engine 100 energy output, to a grid, or to any othersink or consumer of energy produced by the inventive heat engine 100. Asshown in FIGS. 3A-3M, the heat engine 100 is constructed upon a framehaving the representative and exemplary dimensions, and within a housingon the frame. Access and connection points are provided external to thehousing as indicated, in order to facilitate installation, operation andmaintenance. FIGS. 3B-3E indicate the various operative connections tothe inventive heat engine 100 including the waste heat source supply 19,cooling water supply, and water heat source and cooling water returnlines (FIG. 3B); instrument air supply 29 and a mass management (workingfluid) fill point 21 (FIG. 3C); expander 3 air outlet and pressurerelief valves exhaust 22 (FIG. 3D); and CO₂ pump vent 30, high pressureside vent 23, and additional pressure relief valve exhaust (FIG. 3E).Adequate ventilation, cooling via radiators 4 as required andsound-proofing is also accommodated by the housing design. The principlecomponents of the system are indicated on FIG. 3M and illustrated pipeconnections. The variable frequency drive (VFD) 11, programmable logiccontroller (PLC) and electrical power panel (Power Out) areschematically illustrated as installed within the housing.

Also included on or off the skid, or otherwise in fluid or thermalcommunication with the working fluid circuit of the system, is at leastone waste heat exchanger (WHE) 5 (also shown in FIG. 1). The WHE uses aheat transfer fluid (such as may be provided by any suitable workingfluid or gas, such as for example Therminol XP), which is ported to theWHE 5 from an off-skid thermal source, through the exterior of the skidenclosure through a waste heat source supply port 19, through the WHE 5circuit to a waste heat source return 20 exiting the housing (FIGS.3A-3E). In the preferred embodiment, heat is transferred to the systemworking fluid in the waste heat exchanger 5. The working fluid flow andpressure entering the expander EXP 3 may be controlled by the start,shutoff and bypass valves and by the control system provided herein.Also provided is a cooler 12, where additional residual heat within theworking fluid is extracted from the system, increasing the density ofthe working fluid, and exits the cooler 12 and into the System Pump 9.The cooler 12 may be located on or off the skid.

Supercritical working fluid exits the pump 9 and flows to therecuperator (REC) 6, where it is preheated by residual heat from the lowpressure working fluid. The working fluid then travels to the waste heatexchanger (WHE) 5. From WHE 5, the working fluid travels to the expander(EXP) 3. On the downstream side of the EXP 3, the working fluid iscontained in a low pressure side of the cycle. From the EXP 3 theworking fluid travels through the REC 6, then to the cooler 12 and thenback to the Pump 9.

Suitable pressure and temperature monitoring at points along the linesand at the components is provided and may be integrated with anautomated control system.

A control system can be provided in operative connection with theinventive heat engine system 100 to monitor and control the describedoperating parameters, including but not limited to: temperatures,pressures (including port, line and device internal pressures), flowmetering and rates, port control, pump operation via the VFD, fluidlevels, fluid density leak detection, valve status, filter status, ventstatus, energy conversion efficiency, energy output, instrumentation,monitoring and adjustment of operating parameters, alarms and shut-offs.

As further described, a representative control system may include asuitably configured programmable logic controller (PLC) with inputs fromthe described devices, components and sensors and output for control ofthe operating parameters. The control system may be integral with andmounted directly to the inventive heat engine 100 or remote, or as partof distributed control system and integrated with other control systemssuch as for an electrical supply grid. The control system isprogrammable to set, control or change any of the various operatingparameters depending upon the desired performance of the system.Operating instrumentation display may be provided as a compositedashboard screen display of the control system, presenting textual andgraphic data, and a virtual display of the inventive heat engine 100 andoverall and specific status. The control system may further includecapture and storage of heat engine 100 operational history and ranges ofall parameters, with query function and report generation.

A control system and control logic for a 250 kW nominally net powerrated Thermafficient Heat Engine 100 of the disclosure may include thefollowing features, functions and operation: automated unmannedoperation under a dedicated control system; local and remote humanmachine interface capability for data access, data acquisition, unithealth monitoring and operation; controlled start-up, operation and shutdown in the case of a loss of electrical incoming supply power or powerexport connection; fully automated start/stop, alarm, shut down, processadjustment, ambient temperature adjustment, data acquisition andsynchronization; a controls/power management system designed forinterfacing with an external distributed plant control system.

An exemplary control system for the thermafficient heat engine 100 mayhave multiple control states as depicted in FIG. 4A, including thefollowing steps and functions. Initial fill of a working fluid at 41 topurge and fill an empty system allowing system to warm for startup.Top-up fill at 47 to add mass to the mass management tank(s) while thesystem is in operation. Standby at 40 for power up of sensors andcontroller; no fluid circulation; and warm-up systems active ifnecessary. Startup at 42. Recirculation idle at 43 with fluidcirculation with turbine in bypass mode; gradually warming uprecuperator, cooling down waste heat exchanger; BPVWHX initially open,but closes as hot slug is expelled from waste heat exchanger. Minimumidle at 44, with turbine at minimum speed (.about.20 k RPM) to achievebearing lift-off; Turbine speed maintained (closed-loop) through acombination of pump speed and valve 24 position. Full speed idle at 45,with turbine at design speed (40 k RPM) with no load; Pump speed setsturbine speed (closed-loop). Operation at 46, with turbine operating atdesign speed and produced nominal design power; switch to load controlfrom pump speed control by ramping up pump speed while using powerelectronics 1 load to maintain turbine speed at 40 k RPM. Shutdown at48, with controlled stop of the turboexpander 3 and gradual cooling ofthe system. An emergency shutdown at 49, for unexpected system shutdown;the pump 9 and turboexpander 3 brought down quickly and heat exchangersallowed to cool passively, and venting at 50 to drain the system andremove pressure for maintenance activities.

As schematically illustrated in FIG. 5A, to fill working fluid into theworking fluid circuit of a waste heat recovery or heat engine system asdescribed with a working fluid such as CO₂, the disclosure furtherincludes a working fluid supply which is connected in various ways tothe waste heat recovery/heat engine as described. In one form, a workingfluid supply is contained in a working fluid supply tank, also referredto herein as a “fill storage tank” or “fluid supply tank”, which in oneembodiment may be in the form of a dewar D, as may be commerciallyprovided by a gas or chemical supplier. A pressure differential betweena dewar D (e.g., a liquid CO₂ holding container) and the working fluidvessel, i.e., mass control tank 7, of the mass management system isutilized. This pressure differential drives the fluid from the dewar Dvia line 51 (referred to herein as the “working fluid supply line”) intoa working fluid vessel such as the mass control tank 7 or “massmanagement vessel”. In a preferred embodiment the working fluid is CO₂and as a result, during operation at certain pressures and temperatures,as the working fluid is going to the mass control tank 7 it mayevaporate as it comes in contact with the relatively warmer tank 7; thiscondition continues until the surface of the tank 7 cools to thesaturation temperature for the given tank pressure. The inventive fillsystem may further provide a means for controlling the temperatureand/or pressure of the working fluid within the mass control tank 7,such as via a control valve or vent valve 71 located on the vent line ofthe tank. The dewar D is connected or connectable to the working fluidcircuit via one or more fluid lines, as further described. The dewar Dmay be externally connected to the working fluid circuit of the heatengine, as indicated on FIGS. 5A-5D, or incorporated therein, orenclosed within the skid enclosure. Also, external fittings can beprovided for connection of the dewar to the working fluid circuit of theskid.

A first thermocouple TC1 may be placed at the inlet of the mass storagetank 7, e.g. near the bottom of the tank, and a second thermocouple TC2placed at the top of the tank 7 to indicate when the tank 7 is full. Asthe tank 7 fills the temperature of the tank drops, when the temperatureat the top of the tank is equal to the temperature at the bottom of thetank the tank is indicated as full. A liquid eductor tube or “dip tube”72 is provided to prevent overfilling of the tank. The dip tube 72 comesin from the top of the tank and extends downward to a fill height of thetank 7. This guarantees that the fluid line in the tank 7 will never goabove the lowest or distal end of the dip tube 72 within the tank 7.Once the mass control tank 7 is filled, heaters may be used to bring theliquid CO₂ in the tank 7 up to system pressure.

The working fluid contained within the circulation loop of the heatengine system, that contained in the mass management tank 7, and thatcontained in the storage vessel of the inventive working fluid fillsystem may have different temperatures and pressures. Thus, there is aneed to manage this pressure and temperature differential in order topermit the pressure differential to operate to drive working fluid fromthe fill system to the mass management system of the heat engine.Working fluid which is stored in the fill storage tank may evaporatewhen it comes in contact with the warm metal of the mass managementstorage tank and/or the conduit between the fill storage tank and themass management storage tank. The fluid continues to evaporate until themetal cools to the saturation temperature for the given tank pressure.In a preferred mode of operation the working fluid will be at or aboveapproximately −20 deg F. This corresponds to a pressure of 214.91 psia,which is controlled with a control valve on the vent line of the tank.Once the metal cools the tank then begins to fill with working fluid.Vacuum jacketed pipe may be used to minimize the amount of evaporatedfluid.

FIG. 5B discloses another embodiment of the present invention. In thisembodiment of top feed storage the working fluid liquid is drawn fromthe top of the working fluid (e.g., CO₂) storage vessel (dewar D) viathe working fluid supply line 52 to the mass management tank 7. Aworking fluid pump 55 is placed in the working fluid supply line 52 fromthe dewar D, operative to pump working fluid to the mass control or lowpressure side in the working fluid circuit. Valve V1 is opened andliquid CO₂ flows through the pump 55 and through a purge valve PV. Whenliquid is sensed at the purge valve PV, the purge valve PV is closed andthe fill valve FVL leading to the mass control tank 7 is opened. Thesensing can be done using a thermocouple or other means or devices.Working fluid is then pumped to the mass control tank 7 and allowed tocontinue until a condition is met. This can be but is not limited to, asystem pressure, a totalized amount from a flow meter, or a mass readingon the scale. Once the condition is met, the pump 55 is turned off, andall valves are returned to their home positions. This embodiment furtherincludes a working fluid vapor line 51 which runs from the dewar D tothe working fluid vessel 7 and connected to the working fluid supplyline 52.

FIG. 5C discloses another embodiment of the present invention. In thisembodiment, bottom feed storage indicates the liquid draw is coming fromthe bottom of the CO₂ storage vessel via line 52, and pumped by pump 55to the working fluid vessel 7 for mass control or in other words to thelow side pressure of the system. A suction return line 53 runs from asuction cavity of the pump to the vapor return to of the CO₂ storagevessel. This line keeps the pump suction chamber flooded with liquid CO₂allowing for faster startups, and a less complicated control scheme tooperate. When the auto-fill sequence is initiated, valve V1 is openedand the pump 55 is turned on. Liquid CO₂ is then pumped to the masscontrol tank 7 or skid, and allowed to continue until a condition ismet. This can be but is not limited to, a system pressure, a totalizedamount from a flow meter, or a mass reading on the scale. Once thecondition is met, the pump 55 is turned off, and all valves go back totheir home positions.

FIG. 5D discloses another embodiment of the disclosure in which thefollowing sequence works with both top feed and bottom feed CO₂ storagevessels. Valve 71 is opened, when the pressure in the mass control tank7 (PMC) is below the CO₂ storage vessel (dewar) pressure, and fill valveFVL is opened. Liquid CO₂ is then allowed to flow from the storagevessel to the mass control tank 7. This is allowed to happen until acondition is met. This can be but is not limited to, a system pressure,a totalized amount from a flow meter, or a mass reading on the scale.Once the condition is met, the pump is turned off, and all valves goback to their home positions.

The invention thus disclosed in sufficient particularity as to enablingan understanding by those of skill in the art, the following claimsencompassing all of the concepts, principles and embodiments thusdescribed, and all equivalents.

1. A heat engine system operative to execute a thermodynamic cycle usinga working fluid, comprising: a working fluid circuit having a highpressure side and a low pressure side, and a working fluid comprisingcarbon dioxide contained in the working fluid circuit, wherein at leasta portion of the working fluid is in a supercritical state; a heatexchanger in the working fluid circuit and in thermal communication witha heat source, whereby thermal energy is transferred from the heatsource to the working fluid in the working fluid circuit; an expander inthe working fluid circuit and located between the high pressure side andthe low pressure side of the working fluid circuit and operative toconvert a pressure drop in the working fluid to mechanical energy; arecuperator in the working fluid circuit operative to transfer thermalenergy between the high pressure side and the low pressure side of theworking fluid circuit; a cooler in thermal communication with the lowpressure side of the working fluid circuit and operative to control atemperature of the working fluid in the low pressure side of the workingfluid circuit; a pump in the working fluid circuit and fluidly connectedbetween the low pressure side and the high pressure side of the workingfluid circuit and operative to move the working fluid through theworking fluid circuit; a mass management system fluidly connected to theworking fluid circuit, the mass management system having a working fluidvessel fluidly connected to the low pressure side of the working fluidcircuit; and a working fluid storage tank fluidly connected to the massmanagement system via a working fluid supply line, the working fluidsupply tank being configured to store a working fluid supply anddistribute the working fluid supply to the mass management system. 2.The heat engine system of claim 1, wherein the working fluid supplycomprises carbon dioxide.
 3. The heat engine system of claim 1, furthercomprising a valve in the working fluid supply line.
 4. The heat enginesystem of claim 1, further comprising a first thermocouple in fluidcommunication with the working fluid supply line and arranged proximatethe working fluid vessel.
 5. The heat engine system of claim 1, whereinthe working fluid supply line is fluidly connected to a lower region ofthe working fluid vessel.
 6. The heat engine system of claim 1, furthercomprising a dip tube arranged in the working fluid vessel, the dip tubebeing fluidly connected to the working fluid circuit via a vent line. 7.The heat engine system of claim 6, further comprising a vent valvearranged in the vent line and configured to control the temperatureand/or pressure of the working fluid supply within the working fluidvessel.
 8. The heat engine system of claim 6, further comprising athermocouple in thermal communication with the working fluid vessel andconfigured to indicate when the working fluid vessel is full.
 9. Theheat engine system of claim 1, further comprising a heater in thermalcommunication with the working fluid vessel and configured to increase apressure of the working fluid supply within the working fluid vessel.10. The heat engine system of claim 1, wherein the working fluid storagetank is located external to a housing of the heat engine system.
 11. Theheat engine system of claim 1, wherein the working fluid storage tank islocated within a housing of the heat engine system.
 12. The heat enginesystem of claim 1, further comprising a connection to the working fluidsupply line at an exterior of a housing of the heat engine system. 13.The heat engine system of claim 1, further comprising a working fluidpump fluidly connected to the working fluid supply line and operative topump working fluid supply through the working fluid supply line and tothe working fluid vessel.
 14. The heat engine system of claim 13,further comprising a purge valve arranged in the working fluid supplyline and located between the working fluid pump and the working fluidvessel.
 15. The heat engine system of claim 13, further comprising aworking fluid vapor line fluidly coupling the working fluid storage tankto the working fluid vessel.
 16. The heat engine system of claim 1,wherein the working fluid supply line is fluidly connected to an upperregion of the working fluid storage tank.
 17. The heat engine system ofclaim 15, wherein the working fluid vapor line is fluidly connected toan upper region of the working fluid storage tank.
 18. The heat enginesystem of claim 1, wherein the working fluid supply line is fluidlyconnected to a lower region of the working fluid storage tank.
 19. Theheat engine system of claim 15, further comprising a suction return linefluidly coupling the working fluid pump to the working fluid vapor line.20. The heat engine system of claim 15, further comprising a valve inthe working fluid vapor line.
 21. The heat engine system of claim 1,wherein the working fluid supply contains an amount of working fluidgreater than an amount of working fluid required for operation of theheat engine.
 22. The heat engine system of claim 2, wherein the workingfluid storage tank is a dewar.
 23. A method of converting thermal energyinto mechanical energy, comprising: placing a thermal energy source inthermal communication with a heat exchanger arranged within a workingfluid circuit, the working fluid circuit having a high pressure side anda low pressure side; regulating an amount of working fluid within theworking fluid circuit using a mass management system, the massmanagement system having a working fluid vessel fluidly connected to theboth the high pressure and low pressure sides of the working fluidcircuit; supplying a working fluid comprising carbon dioxide to theworking fluid vessel from a working fluid supply tank fluidly connectedto the working fluid vessel via a working fluid supply line, wherein atleast a portion of the working fluid is in a supercritical state;pumping the working fluid through the working fluid circuit by operationof a pump, the pump being configured to supply working fluid in asupercritical or subcritical state; expanding the working fluid in anexpander to generate mechanical energy, the expander being fluidlycoupled to the pump in the working fluid circuit; directing the workingfluid away from the expander through the working fluid circuit and backto the pump; controlling a flow of the working fluid in a super-criticalstate from the high pressure side of the working fluid circuit to theworking fluid vessel; and controlling an amount of working fluid in asub-critical or super-critical state from the working fluid vessel tothe low pressure side of the working fluid circuit and to the pump. 24.The method of claim 23, further comprising drawing the working fluidfrom the working fluid supply tank to the working fluid vessel by apressure differential between the working fluid supply tank and theworking fluid vessel.
 25. The method of claim 24, further comprisingdrawing the working fluid from an upper region of the working fluidsupply tank.
 26. The method of claim 23, further comprising supplyingthe working fluid from the working fluid supply tank directly to theworking fluid circuit.
 27. The method of claim 26, further comprisingpumping the working fluid from the working fluid supply tank to theworking fluid circuit.
 28. The method of claim 23, further comprisingpumping the working fluid from the working fluid supply tank to theworking fluid vessel.
 29. The method of claim 23, further comprisingsupplying the working fluid to the working fluid circuit in a liquidstate.
 30. The method of claim 23, further comprising controlling a flowof working fluid from the working fluid supply tank to the working fluidvessel by operating at least one valve arranged in a working fluidsupply line.
 31. The method of claim 23, further comprising controllinga temperature and a pressure of the working fluid in the working fluidvessel using a vent valve arranged in a vent line that is in fluidcommunication with the working fluid circuit.